The Spamhaus Project is an international organisation, founded by Steve Linford in 1998, dedicated to tracking email spammers and spam-related activity. It is responsible for a number of widely used anti-spam DNS-based block lists (DNSBLs). Many ISPs use these services to reduce the amount of spam they take on.

Spamhaus put in a request to block all data traffic from German ISP Cyberbunker, aka CB3ROB, best known for helping out torrent site The Pirate Bay. But Cyberbunker has several server racks with a partner of A2B. A2B, as an upstream provider, refused to block the full IP range of Cyberbunker and decided to block only one particular IP address that Spamhaus had identified as a source of spam.

According to Bais, Spamhaus then decided to include the full IP range of all of A2B's customers in its block list. Several companies were practically offline as a result and couldn’t send or receive email.

Finally A2B gave in and decided to remove Cyberbunker from its BGP (border gateway protocol) list, used for exchanging routing information between gateway hosts. Almost immediately, A2B could resume its normal duties. "Spamhaus cannot be its own judge," Bais told Webwereld.

Several years ago, Spamhaus used similar tactics when it put Austrian Registry Nic.at on its block list. Spamhaus demanded that the Austrian Registry delete 15 domains that the spam-blockers considered to be used by phishers, without providing enough evidence to satisfy Nic.at. Nic.at responded that — because of Austrian law — it could not simply delete domains without proof of bogus WHOIS addresses.

Spamhaus's Steve Linford said: "To say that an SBL listing amounts to extortion is the same as being refused entry to a restaurant because you're not properly dressed, and then claiming that you are being blackmailed." ®